Wafer stage for wafer processing apparatus

ABSTRACT

A wafer stage for use in a wafer processing apparatus having a liquid cooling jacket with a built-in coolant liquid circulation path and a ceramic plate as attached onto the liquid cooling jacket and having therein a heater and an electrode for an electrostatic chuck. The wafer stage enables performance of wafer processing while letting a wafer be mounted on the ceramic plate. The liquid cooling jacket enables attachment of the ceramic plate through a gap for circulation of a coolant gas as formed over the liquid cooling jacket, and a heat resistant seal material containing therein an elastic body for sealing the coolant gas between the liquid cooling jacket and the ceramic plate.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This is a continuation of U.S. application Ser. No. 10/087,747,filed Mar. 5, 2002, the subject matter of which is incorporated byreference herein.

FIELD OF THE INVENTION

[0002] The present invention relates generally to wafer stage structuresfor use in wafer processing apparatus, and more particularly to a waferstage suitable for processing at high temperatures (ranging from about200 to 500° C.).

BACKGROUND OF THE INVENTION

[0003] In recent years, certain materials including but not limited toruthenium and its oxides or platinum or the like are thought to be thetop-rated candidates for the capacitor electrode material ofsemiconductor devices of the next generation, owing to congeniality withcurrently available capacitor dielectric films high in dielectricconstant and the like. In addition, materials which are considered to beemployable as gate dielectric films in place of silicon oxides mayinclude zirconium oxides and hafnium oxides or else whereas PZT(Pb(Zr,Ti)O₃) and BST ((Ba,Sr)TiO₃) are being considered for use ascapacitor dielectric films. In this way, various kinds of “new”materials are under consideration for use as prospective semiconductordevice materials. Unfortunately these new materials are thermally andchemically stable in nature and thus stay extremely low in volatility—inthis respect, these are called non-volatile materials among experts inthe semiconductor device art.

[0004] It is thus inevitable for performing etching treatment of thesenonvolatile materials to maintain the temperature of a wafer beingpresently processed at high temperatures. Although in prior known etchprocessing apparatus or equipment it is a standard way that the wafertemperature is set to range from a low temperature of approximately −50°C. up to about 100° C., this temperature range is deemed insufficient inorder to successfully etch the above nonvolatile materials due to thechemical stability thereof. Thus it is required that the nonvolatilematerials be processed or micromachined within a high temperature rangeof from 200° C. to 500° C.

[0005] To realize a processing apparatus for processing wafers at suchhigh temperatures, it is essential to employ a wafer stage capable ofnot only heating up wafers at high temperatures but also performingtemperature control for establishment of a uniform wafer temperaturedistribution while increasing responsibility even in cases where heatinput from a plasma is present.

[0006] A method for controlling the temperature of a wafer beingprocessed with good responsibility is disclosed in Published JapanesePatent Application No. 7-176601 (JP-A-7-176601), wherein a gas gap spaceis provided between a pedestal for support of a wafer and itsassociative heat source and heat sink being provided thereunder forcontrolling the pressure of a gas being introduced into this gas gapspace to thereby control the wafer temperature.

[0007] Another approach is disclosed in JP-A-2001-110885, wherein a heattransfer gas chamber capable of sealing and exhausting gases is providedbetween a support member for holding a wafer and a cooling member forperforming cooling while further providing a heating element(s) on thesupport member side to thereby maintain the wafer at a high temperature.

SUMMARY OF THE INVENTION

[0008] With the example taught from the above-identified Japanesedocument JP-A-7-176601, in order to seal a gas in a gap space asprovided between the pedestal for support of a wafer and the heat sink,the pedestal and heat sink are welded together; or alternatively, theseare fixed with an O-ring interposed therebetween. In case the pedestaland heat sink are fixed together by welding techniques, whenever thewafer-supporting pedestal is replaced with a new one due to its lifetimeor accidental failures or the like, a replacement range tends to becomewider resulting in an increase in complexity of works required therefor.Additionally the connection due to welding suffers from a limitation tousable materials—that is, both the pedestal and the heat sink arestrictly required to be made of metals only. Alternatively in the caseof fixation using the O-ring interposed, a usable temperature range islimited by the heat resistance temperature of such O-ring so that itsupper limit stays merely at 200° C., or more or less.

[0009] The example found in JP-A-2001-110885 is similar to that ofJP-A176601 in that it discloses therein a method for welding together asupport member for support of a wafer and a cooling member oralternatively clamping them together using bolts with an O-ringsandwiched therebetween, wherein this approach suffers from similarproblems to those stated supra.

[0010] Additionally with this example, a method for improving a waferin-plane temperature distribution is shown, wherein, for the purpose ofimproving the uniformity of a wafer temperature in the area of a wafersurface, a region with a variable height is provided within the regionof a recess portion as provided in a cooling member causing thermalconductance between the cooling member and support member to have adistribution, thereby to improve the wafer in-plane temperaturedistribution. However, with such an arrangement, in the event that acooling member structure capable of realizing an optimized temperaturedistribution is employed in the case of a certain use temperature, thewafer in-plane temperature distribution can often vary at other usetemperatures. This phenomenon poses a serious problem in particular inthe case of usage at a high temperature of 400° C. or 500° C. This canbe said because heat release or “escape” of via radiation from the waferstage relatively increases in the temperature region of 400° C. or 500°C. and thus serves as the cause of deterioration of the wafer in-plantemperature distribution. Inherently it is desirable that thetemperature distribution of the wafer stage be kept uniform in a widetemperature range. To this end, it is advantageous that such heatrelease from the wafer stage is less whereas heat delivery between itand the cooling member stays uniform in the plane. However, in thisexample, no teachings are found as to methodology for suppressing theheat release from the wafer stage. The present invention was made inview of these problems to provide a wafer stage capable of uniformlymaintaining the temperature distribution of a wafer at high temperatureswithin a wide temperature range. The invention also provides a waferprocessing method with virtually no risks of giving obstruction to thewafer due to a temperature change during wafer processing using thewafer stage.

[0011] To solve the foregoing problems the present invention employs thefollowing means.

[0012] In a wafer stage suitable for use in a wafer processing apparatuswhich comprises a liquid cooling jacket with a built-in coolant fluidcirculation path and a ceramic plate that has therein a heater and anelectrode for electrostatic chuck use and is attached to overlie theliquid cooling jacket and which is operable to perform wafer processingwhile letting the wafer be mounted on the ceramic plate, the liquidcooling jacket is arranged so that the ceramic plate is attached througha coolant gas circulating gap as formed on or above the liquid coolingjacket while letting heat-resistant seal materials be disposed betweenthe liquid cooling jacket and the ceramic plate, the seal materialscontaining therein an elastic or resilient body or bodies for sealingthe coolant gas. The ceramic plate is attached to the liquid coolingjacket by more than one adhesive clamping element made of zirconiaceramic material in accordance with a feature of the present invention,and any one of the heater and the electrode for electrostatic chuckincludes a cylindrical plug as built in the ceramic plate and astem-like terminal with a spring member insertable into the cylindricalmember being engaged therewith, in accordance with another feature ofthe present invention.

[0013] Other objects, features and advantages of the invention willbecome apparent from the following description of the embodiments of theinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a diagram showing a first embodiment of the presentinvention.

[0015]FIG. 2 is a diagram depicting an enlarged view of a wafer stageshown in FIG. 1.

[0016]FIG. 3 is a diagram showing a perspective view of a water-coolingjacket.

[0017]FIGS. 4A and 5B are diagrams each showing an enlarged view of aninternal electrode.

[0018] FIGS. 5A-5B are diagrams each showing an enlarged view of aninternal electrode.

[0019]FIG. 6 is a diagram for explanation of the structure of a modulefor supplying electrical power to a heater.

[0020]FIG. 7 is a diagram for explanation of the structure of anelectrical power feed unit for the internal electrode.

[0021]FIG. 8 is a diagram for explanation of a terminal or a shaft alongwith a spring member as engaged at part adjacent to the distal endthereof.

[0022]FIG. 9 is a diagram for explanation of a ceramic plate temperaturemeasuring method.

[0023]FIG. 10 is a graph showing a relationship of a heater outputversus wafer temperature.

[0024]FIG. 11 is a flow diagram for explanation of an automatic waferprocessing condition prediction procedure.

[0025]FIG. 12 is a diagram showing a second embodiment of thisinvention.

[0026]FIG. 13 is a diagram showing a third embodiment of the invention.

[0027]FIG. 14 is a diagram showing a fourth embodiment of the invention.

[0028]FIG. 15 is a diagram showing the fourth embodiment of theinvention.

[0029]FIG. 16 is a diagram showing a fifth embodiment of the invention.

[0030]FIG. 17 is a diagram showing a sixth embodiment of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] Preferred embodiments of the present invention will be explainedwith reference to the accompanying drawings below. A first embodiment ofthis invention is shown in FIGS. 1 and 2. FIG. 1 depicts an examplewherein a wafer stage of the invention is applied to a plasma processingapparatus; FIG. 2 shows an enlarged view of the wafer stage shown inFIG. 1; and, FIG. 3 is a perspective view of a water-cooling jacket.

[0032] As shown in FIG. 1, an etching gas 11 is introduced into theinterior space of a vacuum chamber 9 while maintaining the chamberinterior at an appropriate pressure by open-degree adjustment of a valve12 that is installed in the upstream of a turbo molecular pump 13. Abell jar 10 made of alumina is stacked at upper part of the vacuumchamber 9, with a coil 7 mounted around this bell jar. The coil 7 isconnected to a high-frequency power supply 8 for application of ahigh-frequency voltage, e.g. high-frequency voltage of 13.56 MHz, toboth ends of the coil to thereby create an inductively coupled plasma(ICP) 6. Etch processing is carried out by exposing a wafer 1 to thisplasma. During processing, the wafer is stably mounted on a wafer stage2 while being under temperature management.

[0033] Additionally, in order to apply a bias voltage to the wafer, ahigh-frequency power supply 5 is connected to the wafer stage. Inaddition, a DC power supply 22 is connected to a power feed line of thishigh-frequency power supply for adding electrostatic chuck functionalityto the wafer stage. Note that in the drawing, reference numeral “3”designates a flow rate controller for control of the flow rate of anetching gas whereas numeral 4 denotes a gate valve. The gate valve 4 isset in the open state while the wafer is being transported, therebypermitting a transport arm (not shown) for wafer transportation to moveforward or backward through the gate valve 4.

[0034] A detailed explanation will next be given of the wafer stageembodying the instant invention with reference to FIGS. 2 and 3. Thewafer stage 2 is generally structured from a water-cooling jacket 14 forcooling use and a ceramics plate 15 which has a heater function andelectrostatic chuck function, wherein the plate is rigidly mounted onthe jacket 14 by bolt clamp techniques.

[0035] The ceramics plate 15 is typically made of aluminum nitride thatis large in thermal conductivity, with a heater 16 embedded therein.Thus, supplying power to the heater 16 makes it possible to heat up theceramics plate. It should be noted here that the ceramics plate is madeof aluminum nitride because the aluminum nitride is inherently high inthermal conductivity without risks of creation of any appreciablein-plane temperature differences, which in turn makes it possible tomake uniform or “uniformize” the resultant wafer temperaturedistribution. It would readily occur to those skilled in the art thatthe plate may alternatively be made of other similar suitable materialsin place of the aluminum nitride when the need arises.

[0036] Additionally an internal electrode 17 is provided and embedded tooverlie the heater 16 within the ceramics plate 15, for giving theintended electrostatic chuck function and RF bias to the wafer stage.When applying a DC voltage to this internal electrode 17, a potentialdifference generates between the internal electrode 17 and the wafer 1(this wafer is being exposed to the plasma and is thus keptsubstantially at ground potential), causing electrical charge to beaccumulated or stored between the internal electrode and the wafer'sback surface to thereby allow the wafer to be sucked and fixed byCoulomb force to the ceramics plate. In addition to the DC voltage, ahigh-frequency voltage is also applied to the internal electrode 17,which voltage is for supplying bias power to the wafer. It is thehigh-frequency power supply 5 of FIG. 1 that performs this task.

[0037] An electric circuit is such that the DC power supply 22 forelectrostatic chuck use is connected via a coil 21 to an electricalpower supply or “feed” line 19. In the illustrative embodiment, it is ahollow shaft 20 that corresponds to the power feed line, wherein thehollow shaft is provided within a support member. When applying ahigh-frequency voltage to the internal electrode 17 through this hollowshaft while applying a bias voltage to the wafer, it is possible toeffectively attract ions in the plasma toward the wafer. Whereby,effects are expectable including, but not limited to, an increase inetching rate and further improvements in etching shape.

[0038] An explanation will be given in view of the fact that theobtainable effects are different depending upon layout settings of theheater 16 and the internal electrode 17. An enlarged view of the layoutof an internal electrode 17 similar to the first embodiment is shown inFIG. 4A. In the case of this example the internal electrode 17 isdisposed only within a convex portion or protrusion of the ceramicsplate 15; thus, only the wafer is attracted with the RF bias also beingapplied only to the wafer. In brief, a susceptor 75 is hardlyelectrostatically attracted without application of any RF bias.Accordingly the susceptor 75 will no longer be subjected to plasmaetching. In contrast thereto, in the case of an example of FIG. 4B, asecond internal electrode 76 is built therein, which is electricallyconnected to the ceramics plate's internal electrode 17. With thisscheme, not only the wafer but the susceptor 75 is electrostaticallyattracted while permitting RF bias to be applied also to the susceptor75. To be brief, this scheme provides a method advantageous to etchingprocesses that are strong in deposition properties or characteristics.More specifically in the case of such deposition property-enhancedprocesses, with the scheme of FIG. 4A, deposited materials (sediments)can attach to the susceptor and then these deposits attached behave topeel off to reside on the wafer surface as contaminants in some cases,which in turn causes reduction of production yields. In contrast, in thecase of the FIG. 4B example, any deposits being attached to thesusceptor may be etched away by application of an RF bias thereto,resulting in a decrease in residual contaminants on the wafer surface;thus, there is an advantage that the yield increases.

[0039] An explanation will next be given of a difference of effectsoccurring due to a difference in heater's outer diameter in conjunctionwith FIGS. 5A-5B. FIG. 5A shows a case where the heater 16 is disposedso that its outer diameter is substantially the same as that of theprotrusion of the ceramics plate in a similar way to that of the firstembodiment. In this case, such arrangement is effective as a scheme forequalizing or uniformizing a wafer temperature distribution in the eventthat the amount of heat input from a plasma is large. More specifically,in case the outer diameter of a heater of FIG. 5B is made larger thanthe ceramics plate's protrusion to an extent that it extends and reachesa nearby portion of the outer diameter of ceramics plate, it is possibleto uniformly heat up almost the entire surface area of the ceramicsplate; thus, there is a merit that the wafer temperature distribution isreadily made uniform in the event that there is no plasma heat input oralternatively such heat input stays less. However, in case the plasmaheat input is significant, a need is felt to force the ceramics plate todecrease in temperature; due to this, it is necessary to lessen anoutput toward the heater. In this case the input heat amount of theprotrusion becomes relatively larger than the input heat amount at ornear the outer periphery. This would result in a relative decrease inwafer outer periphery temperature, which leads to creation of atemperature distribution within the wafer surface concerned.

[0040] By contrast, in the case of FIG. 5A, the heater is substantiallythe same in range as the protrusion region with a wafer temperaturedistribution being made uniform by this heater layout whereby an inputheat distribution of only the same region as its original state isobtainable even in cases where the plasma input heat stays large and theheater output decreases so that the resulting wafer temperaturedistribution will no longer be deteriorated.

[0041] It should be noted that with regard to the structure of theaforesaid internal electrode and the heater's outer diameter, these maybe optimized on a case-by-case basis in accordance with conditions foractual implementation. Also note that the present invention should notbe interpreted to restrict the way of employing them in either one ofthe combinations.

[0042] It is apparent that from the above discussion when applying abias voltage to the internal electrode to thereby process the wafer ofinterest, this wafer increases in temperature due to heat input from aplasma. Although such temperature increase poses no specific problems asfar as the input heat amount stays less, failure to perform precisewafer temperature control management in standard or ordinarysemiconductor fabrication processes can result in deterioration ofresultant etching characteristics. As stated previously, in order tomaintain the wafer's temperature at high temperatures, it is necessaryboth to heat up the ceramics plate by the heater in the absence of anyappreciable heat input from the plasma, and to remove the incident heatenergy to the wafer when the processing gets started and there iscertain heat input from the plasma. As a remedy for this, with thisembodiment, as shown in FIG. 2, a gap 18 of 0.5 mm is provided betweenthe ceramics plate 15 and the water-cooling jacket 14 with a helium gaswith a pressure of 1 kPa or below being introduced into this gap.Numeral 23 indicates a helium gas introduction or “inlet” port whereas24 is a helium gas exhaust or “outlet” port. To be brief, when it isrequired to maintain the wafer at high temperatures in the absence ofany heat input from the plasma, close a valve 25 while opening a valve26 to thereby let a pressure within the gap be the same as that of theprocessing chamber (customarily set at about several Pa or less), thusestablishing vacuum thermal insulation. Alternatively when a need arisesto cool down the ceramics plate due to heat input from the plasma, openthe valve 25 and simultaneously close the valve 26 for introduction of ahelium gas into the gap to thereby provide a heat transfer from theceramics plate toward the water cooling jacket, thus performing cooling.In such case, the helium gas residing within the gap is set at anappropriate level in such a way that a pressure gauge 27 is provided inthe downstream of the valve 25 while controlling an operation of a flowrate controller 28.

[0043] Additionally since the pressure of the processing chamber forprocessing the wafer is set at about several Pa or below as describedabove, it is also required to introduce a heat transfer gas such ashelium gas into a space between the wafer back surface and the ceramicsplate. In this embodiment the gas is supplied through the hollow shaftas built in a support member for applying both a high-frequency voltageand DC voltage to the internal electrode. In brief, it is arranged sothat the required helium gas is introduced onto the wafer back surfacefrom a through-going hole 29 which is provided at a central portion ofthe ceramics plate.

[0044] A groove 46 is provided in the interior of the water coolingjacket for forcing water to circulate therealong for cooling purposes.In this embodiment the cooling water as used therein is coolant waterthat is provided within a clean room. Flowing the coolant water into thegroove and water drainage are done by use of more than one flexible pipe(not shown). Piping between the valve 25 and the helium gas inlet port23 employs a flexible pipe 30. With such an arrangement, it is possibleto accommodate upward and downward movements of an entirety of the waferstage 2. Note here that the coolant water inlet port alone is depictedin the drawing with its associated return side eliminated from theillustration. Also note that although in this embodiment water is usedas the refrigerant, this should not be limited only to water. Othersimilar suitable coolants are usable, which include but not limited toflon-based (fluorine-based) refrigeration media such as Florinert andGalden (both are trade names). Note however that in the case of usingwater, in view of the fact that a heat transfer coefficient between acomponent for letting the refrigerant circulate (in this example, thewater cooling jacket) and refrigeration media is significant, there is amerit that an increased heat transfer amount is made available betweenit and the ceramics plate in case a helium gas pressure of the gap 18 iskept unchanged. This may be reworded in a way such that the pressurerequired to provide the same heat transfer amount is lowered. Insummary, the helium's seal conditions are loosened or “relaxed” in termsof apparatus designs; thus, this becomes a great merit.

[0045] Wafer transportation may be done by a process including the stepsof letting the wafer stage 2 move upward and downward owing to expansionand shrink operations of bellows 35 due to up/down mechanisms (notshown) and then peeling off the wafer from the ceramic plate by using apusher pin 32 that is fixed.

[0046] An explanation will next be given of a remedy that is a principalfeature of the present invention, which is for control of a wafertemperature over a wide temperature range covering up to a hightemperature of about 500° C. while at the same time increasingresponsibility and also achieving a uniform distribution.

[0047] As in the illustrative embodiment, in case a helium gas isintroduced into the space between the ceramics plate and the watercooling jacket, it becomes an important technical issue to suppress anypossible leakage of the helium gas. With this embodiment, in order tomake it possible to use the wafer stage up to a high temperature regionof about 500° C., one or more metallic seals each internally holding acoil spring are employed rather than O-rings as used in the prior art.For example in FIGS. 2 and 3, reference numerals 31 and 31′ designate aseal and a seal engagement/insert groove for prevention of leakage fromthe outer periphery of the water cooling jacket 14 toward the processingchamber. In addition, a seal 33 that is less in diameter and has asimilar function and its associative seal insert groove are used aroundthe pusher pin 32 that is for peeling off a wafer out of the stage andthen transport it. Additionally provided around a heater power feed unit34 and a sheath thermocouple (not depicted in FIGS. 1-2 and will bediscussed later) for measurement of a temperature of the ceramics plateare seals each having an appropriate diameter matching the size of itscorresponding one of respective components along with seal insertgrooves associated therewith, thereby precluding any possible helium gasleakage. In the case of using such seals of this embodiment, unlikeO-rings, it is possible to attain sufficient utilization up to a hightemperature of 500° C. or more or less. Additionally, when compared tothe case of mere metal seals, several effects and advantages areexpectable, including a decrease in clamping torque due to the elasticaction of the internal coil spring, an increase in tracking continuityof seal effects even when a positional relationship of those members forsealing based on thermal expansion varies slightly, or an ability toachieve the repeated usability. It is also noted that although in thisembodiment the spring as provided within the metal seal is a coilspring, this may be replaced by a plate spring or the like. Importancelies in that the seal is a member which has elasticity as internallyheld therein and which exhibits deformability.

[0048] The next remedy taken therein is to uniformize a temperaturedistribution of the ceramics plate in order to uniform a wafertemperature distribution. To do this, a unique remedy is employed forsuppressing heat conduction through a bolt(s) for fixing the ceramicsplate to the water cooling jacket and outward heat release from theceramics plate to the water cooling jacket or from the side wall of theceramics plate to the vacuum chamber by radiation.

[0049] One example is that with the present invention bolts 36 made ofzirconia ceramics are used to lower local heat release or “runaway”occurring due to thermal conduction through the bolt(s) for fixing theceramics plate to the water cooling jacket 14. The zirconia ceramics isvery low in thermal conductivity to an extent that the heat conductivityis as small as about 3W/mK and yet significant in value of robustnessagainst destruction to thereby exhibit excellent features as tomechanical strength. Thus this material is suitable for use as thematerial of bolts for fixation of the ceramics plate.

[0050] It should be also noted that this embodiment comes with aspecific design for enlarging the diameter of a bolt hole as provided inthe ceramics plate to an extent that permits thermal expansion of theceramics plate to thereby ensure that any ceramics screw will no longerbe broken even in cases where the ceramics plate is heated up to a hightemperature of about 500° C. This will be explained in detail using apractical example thereof. In this embodiment the zirconia bolt is a M4screw, which is designed to be fixed at a position with a radius of 110mm. In the event that the ceramic plate is heated from a roomtemperature of 20° C. up to 500° C., the resulting expansion due to heatin a radial direction is expected to measure (500−20)×5×10−6×110=0.26 mmin view of the fact that the expansion coefficient of zirconia is5×10−6(1/K). Thus it is required that a marginal allowance of 0.26 mm onone side be given in minimum: in this case, it becomes 4.52 mm. However,it is actually set at +5 with an assembly allowance added thereto.

[0051] Next, for the purpose of preventing outward heat release viaradiation from the ceramics plate, the water cooling jacket has itssurface 37 with mirror polishing or grinding treatment applied thereto.Now estimate the heat release in case the water cooling jacket's surfaceis subjected to the mirror polishing along with that in case of no suchpolishing. In this embodiment the ceramics plate was 240 mm in diameter.Thermal emissivity on the surface of the ceramics plate measures 0.8whereas thermal emissivity on a surface of the water cooling jacket is0.3 in the state that it was not subject to any mirror polishing and 0.1in the state that it experienced the mirror polishing. Measurement ofthe thermal emissivity is executable by direct methods for measuring thethermal emissivity while heating up a specimen or alternatively byindirect methods for calculation based on a spectral reflection factoras obtained through measurement of reflection spectrum using a FT-IR(Fourier transform infrared spectrometer). The water cooling jacket iscooled down and is kept at 30° C., wherein in case the ceramics plate'stemperature is held at 500° C., an increased amount of heat as large asabout 250W will be expelled in the case of no polishing. In contrast, incase the mirror polishing is done, it is lowered to an extent equal toabout 90W, which is roughly ⅓ of the former.

[0052] Next, in order to lower heat release from the outer periphery ofthe ceramics plate, this embodiment is arranged to provide a radiantheat insulating material 38 with chromium plating applied to its surfacein such a manner as to surround the ceramics plate. Now let's estimatean effect of the above-stated radiant heat insulation material. In thisembodiment the ceramics plate was 20 mm in thickness. While in theabsence of any radiant heat insulation material a relatively largeamount of radiant heat of approximately 80W is expelled toward the innerwall (with its thermal emissivity assumed to measure 0.3) of a vacuumchamber with its temperature kept at about a room temperature (assume itto be 25° C.), the same is reduced to measure about 30W in the presenceof the radiant heat insulation material (assume the thermal emissivityon its surface to be 0.1), wherein the latter value is less than half ofthe former.

[0053] It must be noted that although in this embodiment a specificstructure is employed wherein the water cooling jacket's upper surfaceis mirror-polished whereas the radiant heat insulation material ischromium-plated on the surface thereof, such combination will notnecessarily be employed in every case. Both of them may be subject tochromium-plating treatment or alternatively to mirror-polishing. Alsonote that although no specific micro-machining is applied to the surfaceof the ceramics plate, it will also possible that a surface on this sideis also coated with certain material which serves to reduce the thermalemissivity thereon. Further note that although in this embodimentchromium plating is applied as the plating treatment, this inventionshould be limited only thereto and other similar suitable materials arealternatively employable, such as for example nickel or copper or else.Furthermore, although in this embodiment the radiant heat insulationmaterial consists of a single one at the outer periphery of the ceramicplate, the invention should not exclusively be limited thereto: if astructure is used with a plurality of ones stacked over one another,then the resultant heat insulation effect may be further enhanced, whichin turn makes it possible to expect an effect of further uniformizing atemperature distribution in close proximity to the outer periphery ofthe ceramic plate.

[0054] An explanation will next be given of the structures of electricalpower feed units one of which is for supplying electrical power to theheater 16 and the other of which supplies power to the internalelectrode 17 in the first embodiment of the instant invention, withreference to FIGS. 6 to 8. Reference is initially made to FIG. 6 forexplanation of the electrical power feed unit that is operable to supplypower to the heater. A through-going hole 39 is provided in the watercooling jacket 14 with an insulation-use ceramic pipe 40 inserted intothis through-hole for tight engagement therewith. An electrical plug 41is embedded in the ceramics plate 15 at a selected locationcorresponding to the through-hole of the water cooling jacket and iselectrically conducted to the inside heater 16. A terminal 42 isattached through the ceramic pipe in the form of being inserted intothis electrical plug. At a portion near distal ends of the terminal andshaft, a spring member 43 which was formed by bending a spiral-shapedconductor as shown in FIG. 8 into a circular shape is immovably engagedand mated in order to ensure establishment of reliable contact betweenthe terminal and the electrical plug. Numeral 44 is a seal forprecluding leakage of helium gases residing within the gap 18. 45 is awiring, which is connected to an external heater power supply. Althoughin this embodiment the heater power feed unit as disclosed hereinconsists of a single one, two power feed units are employed when theinvention is reduced to practice due to a necessity of using a pair ofconnectors of the opposite polarities.

[0055] An explanation will next be given of the structure of the powerfeed unit for supplying power to the internal electrode 17 withreference to FIG. 7. A through-hole is defined at a central portion ofthe water cooling jacket, with a ceramic pipe 48 for insulation purposesbeing embedded therein. A shaft 20 and a dielectric pipe 47 made ofpolytetrafluoroethylene for electrical insulation use are inserted intothis ceramic pipe. Provided adjacent to a distal end of the shaft is aspring member 43 for making sure electrical contact in a similar way tothat of the heater power feed unit. A guide 50 that is fixed by bolts 49to an electrical plug 51 as embedded in the ceramics plate 15 is coupledthrough the spring member 43 to the shaft 20. The electrical plug 51 iselectrically connected to the internal electrode 17; with such a route,it is possible to apply an electrostatic chuck-use DC voltage andhigh-frequency bias voltage to the internal electrode. Numeral 52denotes a seal for sealing helium gases.

[0056] In this way, since the connection structure of part being formedwithin the ceramics plate to supply electrical power to the internalelectrode and the heater is arranged as a structure for connection froma lower side of the ceramics plate through the spring member, it ispossible to readily perform any intended attachment and detachment ofthe ceramic plate. In addition, as it utilizes elastic deformation ofthe spring, the resultant electrical contact is made more reliable tothereby ensure that any contact failures will no longer occur.Additionally, since the electrical contact in improved in reliabilityowing to the spring's elastic deformation, an effect also is expectableof enabling the intended contact to be sustained even in cases where theceramics plate exhibits thermal expansion at high temperatures resultingin a change in gap between it and the plug side. Thus it becomespossible to realize electrical connection over a wide temperature range.

[0057] An explanation will next be given of a method of measuring atemperature of the ceramics plate as required to determine an output ofthe heater and a helium gas pressure in conjunction with FIG. 9. Athrough-hole 54 is provided at a portion of the water cooling jacket 14,with a recess portion 53 provided in a back surface of the ceramicsplate 15 corresponding to this through-hole. The recess has a diameterwhich is desirably set at a specified value that is equal to thediameter of the sheath thermocouple plus an allowance capable ofpermitting thermal expansion at a maximal use temperature of theceramics plate. For example, suppose that the diameter of the sheaththermocouple is 3 mm, a temperature is 500° C., and the attachmentposition is a position of a radius of 80 mm; if this is the case,resultant expansion from a room temperature of 20° C. is represented as(500−20)×5×10−6×80=0.19 mm in view of the fact that the coefficient ofthermal expansion of zirconia is 5×10−6(1/K). Accordingly, an allowanceof 0.19 mm on one side is required in minimum—in this case, it measures3.38 mm. However, in actual implementation, a value of 4 mm is used withan extra allowance for assembly included therein. Let a sheaththermocouple 55 be inserted in such a manner that its distal end comesinto contact with a back face of this recess. If the contact state ofthe distal end changes then a temperature being measured also changes;to avoid this, in this embodiment, a flange 56 is provided at thethermocouple while letting a coil spring 57 be engaged at a portion ofthis flange with a holder 58 fixed to a support member 59 being employedto push and compress the entirety of the sheath thermocouple against theceramics plate 15.

[0058] Accordingly, a contact pressure of the sheath thermocouple'sdistal end and the ceramics plate is kept constant even when theattachment state of the ceramics plate slightly changes, which in turnmakes it possible to provide the intended temperature measurement methodexcellent in reproducibility.

[0059] Other available ceramics plate temperature measurement methodsinclude a method that utilizes a radiation thermometer. In this case thedistal end of such radiation thermometer may be designed so that it isin non-contact with the ceramics plate; thus, there is an advantage thatany extra mechanism for constantly retaining the contact state is nolonger required.

[0060] With the temperature measurement methodology stated above, it isimpossible to directly measure a temperature of the wafer of interest.However, if a relative relationship between the ceramics plate and awafer temperature is made evident through experimentation in advancethen it is possible to estimate the wafer temperature. In addition thewafer is not required in any way to come into contact with a probe fortemperature measurement use so that there is no risk of an increase inresidual contaminants on the back surface thereof.

[0061] As explained above, in accordance with the arrangement of thisembodiment, it is possible in the case of heating up the ceramics plateto heat up the ceramics plate at high speeds by exhausting gases from anenclosed space of the gap between the ceramic plate and the watercooling jacket to thereby create a vacuum for thermal insulation andthen supplying electrical power to the heater. In addition, in the eventthat heat input is available from a plasma during wafer processing, itis possible to remove the heat input by letting a helium gas flowbetween the ceramics plate and the water cooling jacket, which in turnmakes it possible to retain permit a wafer temperature constantly.Additionally the use of more than one metallic seal with a coil springheld therein in place of O-rings makes it possible to apply the intendedprocessing to the wafer of interest over a wide temperature rangecovering up to a high temperature of about 500° C. Additionally, as theceramics plate is not required to be welded to the water cooling jacket,it is possible to readily replace only the ceramics plate whenever theneed arises.

[0062] It should be noted that although in this embodiment theindividual seal used therein is a seal made of metal with a coil springbuilt therein, the present invention should not be limited only thereto;for example, a seal made of polymer material high in heat resistancetemperature or the like may be used. In this case, it is lower instiffness than metal seals so that an effect is expectable of reducing aclamping torque of bolts for fixation of the ceramics plate.

[0063] In addition, since the bolts for fixation of the ceramics plateare made of zirconia ceramics, the amount of heat releasing or“escaping” through the bolts is reduced enabling electrical power beingsupplied to the heater to be lowered resulting in a likewise decrease inrunning cost. Additionally the heat release from nearby portions of theouter periphery of the ceramics plate is lessened enabling anytemperature drop-down near or around the outer periphery to decreaseaccordingly, which results in preclusion of lack of the uniformity of awafer temperature distribution.

[0064] Additionally the part around the ceramics plate is specificallydesigned to have a structure high in radiant heat insulation effectswhereby it is possible to reduce heater power being fed to the ceramicsplate so that an effect is expectable of suppressing the running costthereof. Additionally heat release due to radiation from the outerperiphery of the ceramics plate may be suppressed or minimized enablingprevention of a temperature dropdown near the outer periphery of theceramics plate resulting in a wafer in-plane temperature distributionbeing made uniform.

[0065] An explanation will next be given of several setup items to beset by workers in case the processing apparatus incorporating theprinciples of the present invention at real manufacturing sites—inparticular, setup items for setting a wafer temperature (e.g. RF biaspower, heater output, helium pressure on wafer back surface, gap'shelium pressure).

[0066] See FIG. 10, which is a graph indicative of a relationship of aheater output versus a wafer temperature in the event that the RF biasis set at 500W in a processing apparatus embodying the invention whilesetting the wafer back face helium gas pressure at 1 kPa, with the gap18's helium pressure as a parameter. This graph may be determined inadvance through experimentation or alternatively calculated bycomputation. Such a graph is to be prepared per each bias power.Accordingly, using this graph makes it possible for workers to readilyestimate or forecast a wafer temperature under certain conditions ofprocessing to be done from now. It is also possible to adversely readtherefrom which values of the heater output and the gap's heliumpressure permits realization of any required wafer temperature; thus itis possible to improve the working efficiency.

[0067]FIG. 11 shows an example with this procedure automated. In thisexample, a worker or operator is first expected to set up his or herdesired processing temperature and a helium pressure on the back surfaceof a wafer plus RF bias power (at step 1). This information is sent to acomputer, which performs arithmetic processing based on its internallyprepared information shown in FIG. 10 (step 2) and then calculates therequired heater output and gap's helium pressure. Results are output toa display unit in case the worker attempts to finally set them manually(step 4). Alternatively in case automatic processing is done based onthe calculation results, control a heater control device and a flow ratecontroller 28 for flowing helium to the gap (step 5).

[0068] An advantage of these methods lies in that the conditions arereadily set in the event that the worker initially implements a newprocess. It must be noted that although the setup items for setting thewafer temperature further include a temperature and a flow rate ofrefrigerant in addition to the above-noted examples, these are withdrawnfrom consideration because of the fact that they rarely pose anyappreciable problems in cases where water is flown as the refrigerant orcoolant at a rate of several liters per minute. However, if under useconditions in certain regions affecting the temperature, then it isimportant in a viewpoint of wafer temperature control procedure to takethem into consideration as setup items in advance.

[0069] As explained above, in accordance with the first embodiment ofthe present invention, it is possible to perform processing with lesspower within a widened temperature range while making the wafertemperature uniform. It is also possible by extending this embodiment toactively change or modify the temperature distribution duringprocessing. This will be explained below.

[0070]FIG. 12 shows a second embodiment of the invention as disclosedand claimed herein. This embodiment is arranged to have a structure inwhich a heater assembly being internally provided in a ceramics plate 60consists essentially of separate or “independent” heaters: an outerperiphery heater 61, and an inner periphery heater 62. In addition,although not specifically depicted in FIG. 12, two sheath thermocouplesare provided at locations in a radial direction for measurement of atemperature adjacent to the inner periphery of a wafer and a temperaturenear the outer periphery thereof. Using these two thermometers makes itpossible to control electrical power being supplied to each heater onthe basis of information as to temperatures as measured thereby. Notethat in FIG. 12, a pusher pin mechanism is eliminated from theillustration for simplification purposes only.

[0071] With such an arrangement, in the event that a temperaturedistribution is required to be generated within a wafer surface, itbecomes possible to readily realize it by changing or updating electricpower being supplied to each heater. Whereby, it becomes possible toobtain any desired etching characteristics.

[0072] Although in this embodiment the heater assembly is subdividedinto two separate regions one of which is adjacent to the center and theother of which is near the outer periphery, it will not necessarilydivided into two portions and may alternatively be designed to havedifferent patterns or still alternatively be divided into threeportions. It is the one that should be adequately determined on acase-by-case basis to realize a required wafer temperature distribution.

[0073] A third embodiment of the invention is shown in FIG. 13. In thisembodiment a recess portion 64 is provided in the gap as providedbetween a water cooling jacket 63 and ceramics plate 15 in such a way asto permit division of an inner periphery and outer periphery whileproviding a mechanism for introduction and outward delivery of heliumindependently of the inner periphery and outer periphery. In thedrawing, only an inside introduction port 65 and outside introductionport 66 are depicted with no helium exit ports shown therein. Note thatthe pusher pin mechanism and heater power feed unit are eliminated fromthe illustration for purposes of simplification only. In thisarrangement, letting the inside region and outside region change inhelium gas pressure makes it possible to permit thermal conductancerelative to the ceramics plate to change accordingly, which in turnenables successful control of the resultant wafer temperaturedistribution. Although in this embodiment no specific seals are providedat the dividing recess portion, it is possible to establish a differencein pressure between the inside and the outside because the conductanceis sufficiently small in value. However, if more than one seal member isprovided at the recess portion where necessary, then it becomes possibleto more precisely control an inside pressure and an outside pressure.

[0074] In each of the above-stated embodiments the helium gas beingintroduced into the space between the wafer back surface and theceramics plate is introduced from a central portion thereof in allcases. However, this arrangement will not be necessarily employed andmay be modified so that the gas is introduced into part adjacent to thewafer's outer periphery or still alternatively introduced from both thecenter and the outer periphery at a time. Which one of them should beused is appropriately determinable from viewpoints of apparatus designeasiness and desirable wafer temperature distributions and the like on acase-by-case basis.

[0075] Optionally, when the second and third embodiments of thisinvention are combined together for actual reduction to practice, itbecomes possible to further effectively control the temperature of awafer being presently processed or the temperature of a wafer(s) withina lot or the temperature of a wafer between lots.

[0076] Also note that although in each embodiment stated supra theelectrostatic chuck for fixation of a wafer is one that employs theso-called monopole scheme with its internal electrode being of a singlepolarity, the invention should not be limited only to this. Morespecifically the internal electrode for use with such electrostaticchuck may alternatively be the one of the type using so-called bipolarscheme having two independent electrodes. With this scheme, there is adisadvantage which follows: the resulting structure is complexed due tothe necessity to make use of two separate electrodes in the interior; oralternatively, two power supply units are necessary. However, since itis possible to attract and stably hold a wafer even in the absence of aplasma therein, in other words, it is possible to introduce coolantgases onto a wafer back surface prior to start-up of the required plasmaprocessing—there is an advantage that excellent temperaturecontrollability is achievable.

[0077] Further note that although the plasma source of the processingapparatus of each of the above-noted embodiments is designed under anassumption that a inductively coupled plasma schemes is used, theinvention should not necessarily be limited thereto. For example, it maybe a plasma source of the type employing parallel planar plate schemesor alternatively UHF plasma, VHF plasma, and ECR plasma are available.Other available examples include plasma processing apparatus of themagnetron type using magnetic fields. Determining which one is selectedfor actual use from among these schemes is done in such a way that acertain one should be employed which matches the characteristics ofactually processed material and thus is appropriately selected on acase-by-case basis.

[0078] An explanation will next be given of a fourth embodiment of theinvention with reference to FIGS. 14-15 below. In cases where asemiconductor wafer is processed at a high temperature such as 500° C.,rapid heat-up of the semiconductor wafer can result in occurrence ofaccidental cracking due to application of thermal shocks. In view ofthis, the embodiment shown herein is arranged so that a process isintroduced of pre-heating the semiconductor wafer while supporting itwithin a prespecified length of time period after having transferred andloaded the wafer onto the wafer stage within a processing chamber. Thetemperature rise characteristic of such semiconductor wafer is shown inFIG. 14 in units of wafer stage temperatures (300° C., 400° C., 500° C).A time constant (“t” seconds) per wafer stage temperature isdeterminable from viewing this diagram.

[0079]FIG. 15 is a flow chart showing a wafer transportation process. Asshown herein, the wafer transfer process includes the steps of loading asemiconductor wafer into a processing chamber (step 11), performingpreheating for a predetermined length of time period which is differentper processing process (for example, the time period of the above-notedtime constant) while immovably holding the loaded semiconductor wafer ona wafer stage (step 12), and mounting the wafer on the wafer stage aftercompletion of the preheating (step 13). Then, apply plasma processing tothe wafer (step 14); after termination of the processing, send the wafertoward a transfer chamber (step 15). Next, introduce a nitrogen gas intothe transfer chamber to thereby cool down the wafer (step 16); afterhaving cooled it to a prespecified temperature, unload the wafer.

[0080] In this way, with this embodiment, the preheat time of apredetermined duration is provided. Although this process increases thewafer processing time per single piece, it is possible to preventoccurrence of unwanted cracking of wafers due to thermal shocks.Consequently with the processing method of this embodiment, it isfinally possible to expect an effect of improving the apparatus inworking efficiency.

[0081] On the other hand, in case the wafer is to be unloaded andtransferred outwardly, a process is required of reducing the wafer'stemperature after having moved the semiconductor wafer from theprocessing chamber to a buffer room (transfer chamber). In view of this,with this embodiment, after having moved it to the buffer room,introduce a nitrogen gas in the state that the wafer is not yet takenout and then let the heat energy move to a chamber of the buffer room tothereby cool down the wafer. Using this method makes it possible toreadily cool the wafer while retaining increased safety even whenoperators touch it accidentally.

[0082] Although the embodiments discussed above are arranged to have aspecific structure with the internal electrode and heater built in theceramics plate, other wafer stages adaptable for high-temperatureetching treatment will be explained below.

[0083] A fifth embodiment of the invention is shown in FIG. 16. In thisembodiment a ceramic heater 69 containing therein a heater wiring 70 anda structure with a sprayed film 68 of ceramics provided on a surface ofan aluminum base material 67 are integrated together by brazingtechniques, which structure is fixed to the water cooling jacket 14using zirconia bolts 36. In this example the sprayed film 68 functionsas a dielectric film for use in the electrostatic chuck. Supplyingelectrical power to the aluminum base material is performed by a shaft20, wherein a coil spring-like spring member is used for an electricalcontact portion between the aluminum base material and the shaft in asimilar way to that in the first embodiment, thus enabling usage withina wide temperature range. Accordingly, by applying a DC voltage and RFbias voltage through the shaft in a similar way to the first embodiment,it is possible to achieve attraction and fixation of the wafer and applythereto the RF (high-frequency) bias. Heat transfer between the ceramicsheater and the water cooling jacket is done by introduction of a heliumgas into a gap 18 in a similar way to that in the first embodiment,wherein the seal for suppression of leakage into the processing chamberis a metallic seal with a built-in structure having elasticity thereinin a similar way to the first embodiment. In addition, a radiant heatinsulation material 38 is provided at outer peripheries of the aluminumbase material and the ceramics heater for preventing outward release orescape of the heat energy via radiation. With such an arrangement,similar effects to those of the first embodiment are expectable; inaddition thereto, an effect is obtainable of enabling fabrication of thedielectric film for use in the electrostatic chuck using spray methodsthat are inherently low in production costs.

[0084] A sixth embodiment of the invention is shown in FIG. 17. In thisembodiment the aluminum base material 67 and the ceramics heater 69 arefixed by zirconia ceramic bolts 36 with an aluminum plate 71 interposedtherebetween. This aluminum plate 71 is used to improve the thermalcontact between the aluminum base material 67 and ceramic heater 69.Thus, it will not necessarily be made of aluminum and may alternativelybe made of any available materials which serve to improve the thermalconduction, such as other metals and heat conductive grease or the like.The ceramic heater 69 is fixed to the water cooling jacket 14 by morethan one ceramics bolt 73. The remaining arrangement is such that thetechniques of the first embodiment are applied in a similar way to thatof the fifth embodiment. Consequently, with such an arrangement, similareffects to those of the first embodiment are expectable; in additionthereto, the dielectric film for use in the electrostatic chuck ismanufacturable by spray methods low in production costs whilesimultaneously permitting easy replacement of only the aluminum basematerial in the event of replacement of the electrostatic chuck due tothe fact that the aluminum base material alone is readily detachable,resulting in a decrease in cost and an increase in maintenanceproperties.

[0085] As apparent from the foregoing, in accordance with eachembodiment of the present invention, it is possible to maintain thewafer of interest with a uniform temperature distribution within a widerange covering from low to high temperatures while suppressing orminimizing any possible temperature variations during processing. Thusit becomes possible to perform etch processing even with respect tononvolatile materials that are inherently incapable of being etched bypresently available standard processes.

[0086] In addition, it becomes possible to actively control thetemperature distribution of a wafer being processed within a widetemperature range of from low to high temperatures. It is possible toprovide a processing method without risks of cracking due to thermalshocks in the case of heating up a wafer up to high temperatures.Further, it is possible to provide a processing method with increasedsafety even in cases where workers touch a wafer of high temperatureswhile the wafer is being unloaded for outward transportation.

[0087] As has been explained above, according to the present invention,a wafer stage is provided which is capable of uniformly maintaining thetemperature distribution of a wafer within a widened temperature range.It is also possible to provide a wafer processing method withoutsuffering from risks of giving temperature change-induced obstruction towafers.

[0088] It should be further understood by those skilled in the art thatthe foregoing description has been made on embodiments of the inventionand that various changes and modifications may be made in the inventionwithout departing from the spirit of the invention and the scope of theappended claims.

What is claimed is:
 1. A wafer stage for use in a wafer processingapparatus comprising a liquid cooling jacket with a built-in coolantliquid circulation path and a ceramic plate as attached onto said liquidcooling jacket and having therein a heater and an electrode for anelectrostatic chuck, said wafer stage being enabling performance ofwafer processing while letting a wafer be mounted on the ceramic plate,wherein said liquid cooling jacket enables attachment of said ceramicplate through a gap for circulation of a coolant gas as formed over saidliquid cooling jacket, and a heat resistant seal material containingtherein an elastic body for sealing said coolant gas between said liquidcooling jacket and said ceramic plate.
 2. The wafer stage according toclaim 1, wherein said coolant liquid circulation path is divided into aplurality of circulating paths which are independent of each other dueto a protrusion provided at said liquid cooling jacket.
 3. The waferstage according to claim 1, wherein said heater as built in said ceramicplate is divided into a plurality of mutually independent heaters. 4.The wafer stage according to claim 1, wherein said liquid cooling jackethas a surface opposing said ceramic plate which is one of mirror surfacemachined and plating treated.
 5. The wafer stage according to claim 1,wherein a radiant heat insulation material having an inner surfacethereof which is one of mirror surface machined and plating treated isdisposed at an outer periphery of said ceramic plate.
 6. The wafer stageaccording to claim 1, wherein said heat resistant seal material is aseal material made of any one of a metal and a heat resistive polymermaterial.